I am planning on building a large bore pneumatic mortar, and I could run it on pressures up to 500 psi. For a barrel, my only easily available material is solid wall, non pressure rated ABS. I know that barrel materials, so long as they are reasonably solid, are not a big concern. However, the pressure in the first few inches of the barrel will exceed the pipe's burst pressure.

I was just wondering if anyone else has used low strength barrels on high pressure pneumatics (or hybrids), and what kind of results they achieved.

I wouldn't trust it, it will fail eventually and thats a promise. My pvc pneumatic rifle which i rarely took past 80psi recently had its barrel explode. unfortunately the only piece of pipe i had left over for the barrel was non-pressure rated (unlike the actual cannon). Lucky no one was standing next to me when it happened. .

The easiest way to figure this out would be to fire it, and just not be there when it happens.
ABS is very shock resistant, but putting 500 psi in something not designed to hold any pressure will probably result in some type of failure. you would be better off using 4" conduit pipe, actually. If you know anyone who works in a large factory of some type you may be able to snag some cheap/free.

supa_midget wrote:I wouldn't trust it, it will fail eventually and thats a promise. My pvc pneumatic rifle which i rarely took past 80psi recently had its barrel explode. unfortunately the only piece of pipe i had left over for the barrel was non-pressure rated (unlike the actual cannon). Lucky no one was standing next to me when it happened. .

Thats a promise?I still am remaining stern on the fact I think it would hold fine. Unless the pipe has a defect or your ammo is too tight.

supa_midget wrote:I wouldn't trust it, it will fail eventually and thats a promise. My pvc pneumatic rifle which i rarely took past 80psi recently had its barrel explode. unfortunately the only piece of pipe i had left over for the barrel was non-pressure rated (unlike the actual cannon). Lucky no one was standing next to me when it happened. .

I've also had 260psi rated pipe explode at 110psi. PVC pipe isn't meant for compressed air but unless it has a defect it shouldn't explode.

As long as you use low friction ammo and do a few test shots first, I think it should be fine.

I have used a lesser pressure rated piece of PVC PN9 for a barrel and it ruptured from the shot,but I think the vibrations/Harmonics has more of a deal to do with the barrel rupturing.Use pressure rated,don't risk it.

Well, there's no such thing as pressure rated PVC or ABS here, and nothing pressure rated at all in sizes over 2.5", which is why I was asking. I have never had an ABS barrel fail in any way, and I have used them on everything from 170 psi pneumatics, to an oxy-MAPP combustion gun. This however, would be more than twice the pressure of either of those, and I would be afraid that the barrel just wouldn't hold.

I think that the problem with exploding PVC barrels has something to do with shock loads more than anything, and I am convinced that ABS is a better barrel material.

If the barrel can't take it, I'll either have to reinforce the barrel somehow, or just keep the pressure down.

Would it make a difference with the barrel concern if the cannon was coaxial? This way, the high pressure would be on the outside of the barrel, and, once it is fired, there would still be pressures on the outside of the barrel which may help to strengthen the inside of the barrel for that brief spike.

DYI: You seem to know a whole lot more than me concerning this stuff so please correct me if I am wrong.

I think that it being coaxial would make it even worse, since, instead of a short spike to about 430 psi (due to all the dead space), it would have 500 psi constantly pushing in on the walls of the pipe, likely destroying it very quickly. Also, coaxials require modifying fittings usually, and I wouldn't trust a modified fitting at 500 psi.

A look on the GGDT shows that by +3 ms the barrel pressure will have spiked to 430 psi, and that by +10 ms it would be down to 125 psi. My parents don't want me shooting any of my large (>100 ci) launchers at over 350 psi anyway, so this may never see 500 psi anyway.

DYI wrote:Well, there's no such thing as pressure rated PVC or ABS here, and nothing pressure rated at all in sizes over 2.5",

sorry but that isn't true i have pressure rated 6 inch sch 80 i just got from the plumbing store for 10$ (the guy cant sell only 7 feet to anyone serious) anyway the pipe has a pressure rating of like 228 written on the side.

Mike, he lives in Canada, and he can't buy anything pressure rated in those diameters. Just a misunderstanding.
DYI, it's really hard to tell if you're barrel is going to explode. I've never had a barrel blow up, even using Sch 40 1/2" at 6x hybrid mixtures. ABS is pretty shock resistant, but in this case, it's just unpredictable. I'd buy 4 feet or something and try that before using a whole 12 foot piece, just in case it did break.